The present invention relates to seals in a gas turbine and particularly to a compliant seal for application at the gas turbine nozzle and shroud interface.
In a gas turbine, hot gases of combustion flow from combustors through first-stage nozzles and buckets and through the nozzles and buckets of follow-on turbine stages. The first-stage nozzles typically include an annular array or assemblage of cast nozzle segments each containing one or more nozzle stator vanes per segment. Each first-stage nozzle segment also includes inner and outer band portions spaced radially from one another. Upon assembly of the nozzle segments, the stator vanes are circumferentially spaced from one another to form an annular array thereof between annular inner and outer bands. A nozzle retaining ring coupled to the outer band of the first-stage nozzles supports the first-stage nozzles in the gas flow path of the turbine. An annular nozzle support ring, preferably split at a horizontal midline, is engaged by the inner band and supports the first-stage nozzles against axial movement.
Each stage of the turbine also includes a plurality of shroud segments arranged in an annular array thereof defining an annular inner surface forming part of the hot gas path. The shroud inner surface is spaced from the tips of the buckets of the turbine rotor. It will be appreciated that the nozzles in conjunction with the shrouds and buckets form a turbine stage.
Warpage during operation and during repair of the nozzle and the shrouds may leave a gap between those turbine components. As a consequence, hot gases flowing through the hot gas path may leak or dissipate through the gap. As a result, the efficiency of the turbine is reduced. In efforts to seal any such gap appearing in the turbine during operation or repair, W-type seals have been provided between the nozzle retaining ring and the shrouds. However, the W-type seals have not proven effective. For example, a W-type seal can be jammed during assembly of the turbine, i.e., by relative radial movement between the nozzle ring and the shrouds during installation. Also, the W-type seal has been observed to crack during operation as a result of low-cycle fatigue. Consequently, there is a need for effectively sealing between the nozzle ring and the shrouds of the stage of a turbine which would tolerate the warpage of the nozzle ring and shroud, eliminate leakage and improve the robustness of the seal at that sealing location.
In accordance with a preferred embodiment of the present invention, there is provided a composite tubular woven seal for disposition between the nozzle retaining ring and the annular array of shrouds of a turbine stage to effectuate a seal, notwithstanding relative movement of the nozzle ring and shrouds during installation and warpage during operation. An annular cavity is formed in one of the axially registering surfaces of the nozzle retaining ring and shrouds, preferably the shrouds, and which cavity provides a seat for the seal. A composite tubular woven seal is disposed in the cavity and bears against the annular sealing surface of the nozzle retaining ring. Thus, when the nozzle retaining ring and shrouds are installed, the composite tubular woven seal is resiliently and compliantly flattened between the axially opposed sealing surfaces of the respective nozzle retaining ring and shrouds to seal between those surfaces. That is, the diameter of the woven tubular seal is greater than the depth of the cavity whereby the compliant seal is flattened in the cavity between the base of the cavity and the opposing sealing surface. Thus, in the event of any warpage or opening of a gap between the nozzle retaining ring and shroud, the compliant seal will expand to provide an effective seal.
The composite tubular woven supplemental seal is compliant as a result of the multiple layers forming the seal. The layers include an inner woven metal core, a fiber material, a metallic foil and a metal outer covering. Preferably, the inner metal core is formed of a woven stainless steel which is surrounded by a silica fiber. The fiber, in turn, is surrounded by a stainless steel metal foil and the outer covering is formed of a braided metal, for example, Haynes 188. Because of the nature of the composite tubular woven seal, the seal is compliant, particularly as a result of the resiliency of the metal core and surrounding silica fiber. Moreover, the metal foil layer surrounding the fiber prevents leakage between the supplemental seal and the sealing surface of the nozzle support ring, while the braided outer covering serves as a protective wear surface. The inner metal core and silica fibers retain the generally circular configuration of the supplemental seal in cross-section such that the seal, when compressed, is preloaded or biased for return to its circular cross-sectional configuration.
In a preferred embodiment according to the present invention, there is provided a turbine comprising a turbine nozzle retaining ring having a generally axially facing first surface and forming part of a turbine stage, a turbine shroud segment having a second surface in axial opposition to the first surface and forming part of the turbine stage, a cavity in one of the retaining ring and the shroud segment, the cavity opening generally in an axial direction and toward another of the retaining ring and the shroud segment and a compliant seal in the cavity including a seal body formed of multiple layers of different materials for compliantly engaging against one of the first and second surfaces opposite the cavity to seal thereagainst.
In a further preferred embodiment according to the present invention, there is provided a gas turbine comprising a turbine nozzle retaining ring having a generally axially facing annular first surface and forming part of a turbine stage, a plurality of turbine shroud segments defining an annular array thereof and an annular second surface in axial opposition to the first surface, an annular cavity in one of the first and second surfaces opening generally in an axial direction and toward another of the first and second surfaces and a compliant seal in the cavity including a seal body formed of multiple layers of different materials for compliantly engaging against another of the first and second surfaces opposite the cavity to seal thereagainst.